Nuclear receptor for oestrogen in the baboon endometrium: detection, characterization and variation in its...

The present paper describes studies conducted to detect and characterize the nuclear receptor for oestrogen in the baboon endometrium. Only 10% of the [3H]oestradiol nuclear receptor complexes were extracted with a 0.5 M-KCl solution. This solubilized receptor migrated as a 4.4S peak during 5-20% sucrose gradient centrifugation. The oestrogen receptor was not bound to oestrogen in the nuclei under normal physiological conditions. Using an unlabelled competitor addition technique with intact nuclei the variation in oestrogen-receptor concentration of baboon endometrium during the menstrual cycle was measured. This concentration increased slightly during the first week of the cycle, being maximal on day 7 before ovulation (2500 molecules/cell), then decreasing gradually, reaching the lowest level (300 molecules/cell) on day 5 after ovulation, where it remained until the end of the cycle.